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Um estudo do imageamento geoelétrico na investigação rasa; A study of the geoelectrical resistivity imaging for shallow investigations

Gandolfo, Otavio Coaracy Brasil
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/09/2007 PT
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Este trabalho trata do estudo detalhado e com profundidade das metodologias de aquisição, processamento e interpretação de dados de caminhamentos elétricos, sob o enfoque de investigações voltadas a objetivos rasos. Nas técnicas de aquisição 2D (caminhamentos) foram utilizados os arranjos dipolo-dipolo, pólo-dipolo, pólo-pólo e Wenner, permitindo comparações quanto à eficácia dos mesmos. Foi testada uma genuína aquisição 3D utilizando o arranjo pólo-pólo, avaliando-se suas potencialidades e limitações. O Schlumberger foi o arranjo empregado para a execução de SEVs que auxiliaram na interpretação e quantificação das seções geoelétricas 2D, principalmente no que se refere à distribuição vertical das resistividades. Os modelos geoelétricos 2D foram obtidos com um programa de inversão de dados (RES2DINV) que, em tese, é capaz de corrigir as distorções observadas nas pseudo-seções de resistividade elétrica aparente correspondentes aos diversos arranjos utilizados no trabalho. Estes modelos constituem imagens que apresentam uma melhor correspondência com a realidade geológica em subsuperfície, o que facilita a interpretação dos resultados. Procurou-se explorar o máximo as potencialidades do programa de inversão...

SnO 2 ceramics with low electrical resistivity obtained by microwave sintering

Gasparotto, Gisane; Bordignon, M. A N; Foschini, C. R.; Gasparotto, Gisele; Aguiar, E. C.; Zaguete, M. A.; Perazolli, L.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 193-200
ENG
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The main aim of this study was to develop dense and conducting SnO 2 ceramics without precipitated phases on the grain boundaries, which was verified using field emission scanning microscopy (FE-SEM) coupled with an energy-dispersive X-ray spectroscopy (FE-SEM/EDS). Two sample groups were investigated, where the first sample group was doped with zinc while the second one was doped with cobalt. The ceramics were prepared using the oxides mixture method and the sintering was carried out in a conventional muffle oven as well as in microwave oven. The results obtained were found to be similar regarding the relative density for the two sintering methods while time and temperature gains were observed for the microwave sintering method. The relative densities obtained were nearly 95%, for the two sintering methods. Concerning the electrical characterization measurements-electric field x current density as well as the environment temperature, the ceramics obtained through the conventional sintering method presented non-ohmic behavior. For the microwave sintered ceramics, we observed an ohmic behavior with electrical resistivity of 1.3 Ωcm for the samples doped with ZnO/Nb 2O 5 and 2.5 Ωcm for that of the samples doped with CoO/Nb 2O 5. The FE-SEM/EDS results for the microwave sintered ceramics indicated a structure with a reduced number of pores and other phases segregated at the grain boundaries...

Quality control based on electrical resistivity measurements

Ferreira, Rui Miguel; Jalali, Said
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2006 ENG
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The electrical resistivity of concrete is one of the main parameters controlling the initiation and propagation of reinforcement corrosion. It is common knowledge that concrete electrical resistivity is mainly dependent on the w/c ratio (pore connectivity), volume and type of cement, temperature and the moisture. This research work studies the effect of specimen shape and temperature of measurement on electrical resistivity measurements of concrete using the four-point Werner electrode. In addition, the estimation of future values based on early age measurements is also studied. Research has indicated that there is a strong relationship between electrical resistivity and durability indicators at a given age. A relationship for the estimation of the electrical resistivity using early age measurements is suggested. Furthermore, it was observed that temperature has a significant influence on the electrical resistivity of concrete. Based on test results, a relationship similar to the Arrhenius equation is also suggested that can be used for conversion of electrical resistivity measurements to a reference temperature. Based on these equations, the electrical resistivity and compressive strength of concrete at 28 days is predicted using values of electrical resistivity of up to 7 days. Errors depend on the equation used but are approximately 5 % for estimates up to 28 days.

Repeated Electrical Resistivity Tomographies in a CALM Site in Livingston Island, Maritime Antarctica

Correia, António M.; Rocha, João; Vieira, Gonçalo
Fonte: European Association of Geoscientists and Engineers Publicador: European Association of Geoscientists and Engineers
Tipo: Artigo de Revista Científica
ENG
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During the years of 2009, 2012, and 2013 several electrical resistivity tomographies (ERTs) were done in a CALM (Circumpolar Active Layer Monitoring) site near the Bulgarian Antarctic Base of St. Kliment Ohridski. The main objective of the ERTs was to try to identify permafrost zones and their extension, as well as their time and space evolution. Geoelectrical methods, in particular ERTs, are very useful for permafrost studies because of the significant increase of the electrical resistivity when the ground is partially or totally frozen and when temperature is lower than 0 degrees celcius. For each ERT made, 40 electrodes in line, spaced by 2 metres each, were used and the apparent electrical resistivity measurements were mathematically inverted to obtain two-dimensional geoelectrical models for each of them. All models show high electrical resistivity values (of the order of tens of thousands of Ω.m). In the CALM site the high electrical resistivities probably correspond to patches of frozen ground but it is not possible to indicate whether it is sporadic permafrost or remnants of seasonally frozen ground yet.

Study of flow in vadose zone from electrical resistivity surveys

Morais,Fernando de; Bacellar,Luis de Almeida Prado; Aranha,Paulo Roberto Antunes
Fonte: Sociedade Brasileira de Geofísica Publicador: Sociedade Brasileira de Geofísica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2008 EN
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Among the indirect methods applied to environmental monitoring, electrical resistivity has played an important role in accessing water flow in the non-saturated zone of the soil and, consequently, aquifer recharge. This work evaluates the influence of some pedo-geomorphologic properties in the infiltration and percolation of water through the superficial soil horizons by means of multitemporal electrical resistivity sections. The experiments were carried out in two areas of distinct pedo-geomorphological characteristics developed on the crystalline basement of southeastern Brazil. The first is situated in a hollow -shaped slope where lixisols predominate; the second, in a nose -shaped slope where well-developed soils (ferralsols ) predominate. The results proved the efficiency of the electrical resistivity method to delimit percolation of tropical soils, even when subtle differences are found in the hydraulic properties of the soil. It was also possible to establish that in the nose slope percolation is faster than in the hollow.

Estimating traveltimes and groundwater flow patterns using 3D time-lapse crosshole ERT imaging of electrical resistivity fluctuations induced by infiltrating river water

Coscia, I.; Linde, N.; Greenhalgh, S.; Vogt, T.; Green, A.
Fonte: Soc Exploration Geophysicists Publicador: Soc Exploration Geophysicists
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
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The infiltration of river water into aquifers is of high relevance to drinking-water production and is a key driver of biogeochemical processes in the hyporheic and riparian zone, but the distribution and quantification of the infiltrating water are difficult to determine using conventional hydrological methods (e.g., borehole logging and tracer tests). By time-lapse inverting crosshole ERT (electrical resistivity tomography) monitoring data, we imaged groundwater flow patterns driven by river water infiltrating a perialpine gravel aquifer in northeastern Switzerland. This was possible because the electrical resistivity of the infiltrating water changed during rainfall-runoff events. Our time-lapse resistivity models indicated rather complex flow patterns as a result of spatially heterogeneous bank filtration and aquifer heterogeneity. The upper part of the aquifer was most affected by the river infiltrate, and the highest groundwater velocities and possible preferential flow occurred at shallow to intermediate depths. Time series of the reconstructed resistivity models matched groundwater electrical resistivity data recorded on borehole loggers in the upper and middle parts of the aquifer, whereas the resistivity models displayed smaller variations and delayed responses with respect to the logging data in the lower part. This study demonstrated that crosshole ERT monitoring of natural electrical resistivity variations of river infiltrate could be used to image and quantify 3D bank filtration and aquifer dynamics at a high spatial resolution.; Ilaria Coscia...

Flexural Properties, Thermal Conductivity and Electrical Resistivity of Prealloyed and Master Alloy Addition Powder Metallurgy Ti-6Al-4V

Bolzoni, Leandro; Ruiz Navas, Elisa María; Gordo Odériz, Elena
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em 01/12/2013 ENG
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A comparison between the properties achievable by processing the Ti&-6Al&-4V alloys by means of two powder metallurgy approaches, precisely prealloyed and master alloy addition, was carried out. Prealloyed and master alloy addition hydride&-dehydride powders characterised by an irregular morphology were shaped by means of cold uniaxial pressing and high vacuum sintered considering the effect of the variation of the sintering temperature and of the dwell time. Generally, the higher the temperature and the longer the dwell time, the higher the relative density and, consequently, the better the mechanical performances. Nevertheless, a higher processing temperature or a longer time leads also to some interstitials pick-up, especially oxygen, which affects the mechanical behaviour and, in particular, lowers the ductility. Although some residual porosity is left by the pressing and sintering route, mechanical properties, thermal conductivity and electrical resistivity values comparable to those of the wrought alloy are obtained.; The authors want to acknowledge the financial support from Regional Government of Madrid through the ESTRUMAT (S2009/ MAT-1585) project and from the Spanish Ministry of Science through the R&D Projects MAT2009-14547-C02-02 and MAT2009-14448-C02-02. The authors want also to thanks the Fraunhofer IFAM-Dresden Institute for the measurements of the thermal conductivity and electrical resistivity

An electrical resistivity model of the southeast Australian lithosphere and asthenosphere

Robertson, K. E.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2012 EN
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A combination of magnetotelluric and geomagnetic depth sounding data were used to attempt to image the electrical resistivity structure of southeast Australia, to investigate the physical state of the crust and upper mantle. A 3D forward model of southeast Australia comprised of regional sets of broadband and long-period magnetotelluric and geomagnetic depth sounding data, over an area of 440 x 300 km2, was used to map broad-scale lithospheric properties. Model results show an order of magnitude decrease in resistivity from the depleted continental mantle lithosphere of the Delamerian Orogen in the west, to the more conducting oceanic mantle of the Lachlan Orogen in the east. The decrease in resistivity in conjunction with a 0.1 km/s decrease in P-wave velocity at depths of 50-250 km, suggest a change in temperature (_T_200_C) due to lithospheric thinning toward the east as the likely cause, in conjuction with a change in geochemistry and/or hydration. A high resolution two-dimensional inversion using data from 37 new and 39 existing broadband magnetotelluric stations mapped crustal heterogeneity beneath the Delamerian Orogen in much greater detail. Lateral changes in resistivity from 10-10 000 m occur over the space of a few kilometres. Low resistivity (_10 m) regions occur at depths of 10-40 km. Narrow paths of low resistivity extend to the surface...

Low electrical resistivity carbon nanotube and polyethylene nanocomposites for aerospace and energy exploration applications

Moloney, Padraig G.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 199 p.; application/pdf
ENG
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An investigation was conducted towards the development and optimization of low electrical resistivity carbon nanotube (CNT) and thermoplastic composites as potential materials for future wire and cable applications in aerospace and energy exploration. Fundamental properties of the polymer, medium density polyethylene (MDPE), such as crystallinity were studied and improved for composite use. A parallel effort was undertaken on a broad selection of CNT, including single wall, double wall and multi wall carbon nanotubes, and included research of material aspects relevant to composite application and low resistivity such as purity, diameter and chirality. With an emphasis on scalability, manufacturing and purification methods were developed, and a solvent-based composite fabrication method was optimized. CNT MDPE composites were characterized via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Raman spectroscopy, and multiple routes of electron microscopy. Techniques including annealing and pressure treatments were used to further improve the composites' resulting electrical performance. Enhancement of conductivity was explored via exposure to a focused microwave beam. A novel doping method was developed using antimony pentafluoride (SbF 5 ) to reduce the resistivity of the bulk CNT. Flexible composites...

Caracterização de coquinas e dolomitos integrando três metodologias distintas : resistividade elétrica, ressonância magnética nuclear (rmn) e porosimetria por intrusão de mercúrio (MICP); Characterization of coquinas and dolomites using three different techniques : electrical resistivity, nuclear magnetic resonance (nmr) and porosimetry by mercury intrusion (MICP)

Gabriel Leal Fiorelli
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/02/2015 PT
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O presente trabalho tem por objetivo caracterizar rochas carbonáticas de afloramento, com propriedades petrofísicas análogas às do pré-sal brasileiro, integrando três ferramentas distintas: Resistividade Elétrica, Ressonância Magnética Nuclear (RMN) e Porosimetria por Intrusão de Mercúrio (MICP) em condições ambientes. As rochas são coquinas Coqueiro Seco da Formação Morro do Chaves, Bacia Sergipe - Alagoas, Brasil, e dolomitos Silurian da Formação Thornton, provenientes dos Estados Unidos. As amostras de rochas foram analisadas variando-se a suas saturações de salmoura/ar/óleo e medindo-se a resistividade elétrica e o tempo de relaxação magnética transversal (T2) em cada nível de saturação. As amostras foram também analisadas quanto à distribuição de gargantas utilizando a técnica de Porosimetria por Intrusão de Mercúrio (MICP). Os resultados de tempo de relaxação obtidos mostram que as estruturas porosas dos dois sistemas rochosos têm características de distribuição de tamanho de poros multimodal. No entanto, as curvas de MICP apresentaram comportamentos distintos. As coquinas e os dolomitos apresentaram ser compostos na maioria por estruturas macroporosas, com uma pequena parcela mesoporosa e microporosa. As curvas de índice de resistividade para o sistema de saturação água - ar apresentaram comportamento linear para as duas rochas. Em contrapartida no sistema de saturação água - óleo...

Feature enhancement from electrical resistivity data in an archaeological survey: the Sapelos hillfort experiment (Boticas, Portugal)

Alves, Mafalda; Bernardes, Paulo; Fontes, Luís Fernando Oliveira; Martins, Manuela; Madeira, Joaquim
Fonte: Society of Photo-Optical Instrumentation Engineers (SPIE). Publicador: Society of Photo-Optical Instrumentation Engineers (SPIE).
Tipo: Artigo de Revista Científica
Publicado em //2015 ENG
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The PoPaTERVA project is developing applied research regarding the comprehension of the multi-layered cultural background of the Terva Valley Archaeological Park, in Boticas, Portugal. One of the main aspects focused on the project is the appliance of remote sensing techniques to enhance non visible archaeological features. An earth resistance tomography (ERT) survey was carried out at the Sapelos hillfort, by the specialized SINERGEO geophysicist’s team, using a Wenner-Schlumberger array. The resulting data was analyzed by the authors in order to extract and verify valid archaeological features regarding the settlement’s structures. There are several adequate systems that can be used to visualize the surveyed data (x, y, z, Ω). However, the authors preferred the open source Visualization Toolkit (VTK) from Kitware Inc., since it supports several visualization and modelling techniques that are useful for interpretation purposes in archaeological contexts: for instance, it is possible to represent the archaeological site as a virtual scale model, which can be freely manipulated. For the Sapelos hillfort, two distinct visualizations were developed to represent the acquired electrical resistivity data. The first one is used to create a comprehensive volume from the surveyed data...

Isochronal study of Al-Mg, Al-Mn, and Al-Mn-Mg alloys using electrical resistivity and thermoelectric power

Luiggi Agreda,Ney José
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2005 EN
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We have studied the phase transformation kinetics occurring in aluminum alloys containing Mn, Mg, and Mn-Mn-Mg by means of electrical resistivity (rho) and thermoelectric power (deltaS). The alloy samples were annealed isochronally at temperatures ranging from ambient temperature to 615 °C. Both rho and deltaS allowed the separation of several stages of transformation associated to either the precipitation or dissolution of phases that occur during the annealing process. The alloys containing Mn show a strong deltaS growth or a marked r drop between 450 °C and 550 °C, linked to the precipitation of the Mn-rich Al6(Mn,FE) equilibrium phase. While the Mg in aluminum generates a series of maxima and minima of both rho and deltaS associated to the pre-established precipitation sequence: GP Zones ® b' phase ® b phase, a combination of effects ensues in the Mn- and Mg-containing alloys, the Mg effect being enhanced at temperatures below 350 °C and that of the Mn striking the same behavior above such temperature. Our study ascertains that the Mg speeds up the precipitation and lowers the activation energy of the Al6(Mn,Fe) phase, the latter having been evaluated by the multiple temperature method.

Coupled stress-strain and electrical resistivity measurements on copper based shape memory single crystals

Gonzalez,Cezar Henrique; Quadros,Ney Freitas de; Araújo,Carlos José de; Morin,Michel; Guénin,Gerard
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2004 EN
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Recently, electrical resistivity (ER) measurements have been done during some thermomechanical tests in copper based shape memory alloys (SMA's). In this work, single crystals of Cu-based SMA's have been studied at different temperatures to analyse the relationship between stress (s) and ER changes as a function of the strain (e). A good consistency between ER change values is observed in different experiments: thermal martensitic transformation, stress induced martensitic transformation and stress induced reorientation of martensite variants. During stress induced martensitic transformation (superelastic behaviour) and stress induced reorientation of martensite variants, a linear relationship is obtained between ER and strain as well as the absence of hys teresis. In conclusion, the present results show a direct evidence of martensite electrical resistivity anisotropy.

Role of volume versus defects in the electrical resistivity of lattice-distorted V(001) ultrathin films

Huttel, Yves; Cerdá, J. I.; Martínez, J. L.; Cebollada, Alfonso
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 340590 bytes; application/pdf
ENG
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4 nm thick V layers grown by triode sputtering on MgO(001) single crystals and capped with MgO exhibit a perfect epitaxy accompanied by a tetragonal distortion and an unexpected volume compression that increases with the V deposition temperature. The electrical resistivity follows a deposition temperature dependence with these structural modifications, decreasing by an order of magnitude across the temperature range studied. Total energy ab initio calculations rule out electronic structure changes and/or oxygen interface diffusion as responsible for the structure variation. Calculations of the ballistic conductance for the epitaxial V films do not reproduce the resistivity-volume correlation, implying a diffusive electron transport mechanism in the films, despite their high crystallinity. Instead, we assign the origin of the electrical behavior to the presence of growth induced defects in the V lattice, whose density is higher in films deposited at low temperature, and decreases as deposition temperature increases. These results extend the previous findings in volume expanded H loaded Fe/V and Mo/V superlattices to simpler structures where the H content is negligible and, additionaly, all the electronic transport is confined within the V film.; Work performed with partial financial support from the Spanish Commission of Science and Technology. Y.H. thanks the “Ramón y Cajal” program and Consejo Superior de Investigaciones Científicas (CSIC) for financial support. J.C. acknowledges financial support from the Spanish MCyT under Contracts Nos. NAN2004-09125-C07-06 and MAT2007-66719-C03-02. A.C. and Y.H. acknowledge financial support from the Spanish MCyT under Contract No.MAT2005-05524-C02. Elisa Román is gratefully acknowledged for stimulating scientific discussions. The Comunidad Autónoma de Madrid (CAM) under project number S-0505/ MAT/0194 NANOMAGNET is also acknowledged.; Peer reviewed

Temporal monitoring of the waste landfill contamination plume in Rio Claro (São Paulo, Brazil) using geophysical resistivity method; Monitoramento temporal da pluma de contaminação no aterro de resíduos urbanos de Rio Claro (SP) por meio do método geofísico da eletrorresistividade

Bortolin, José Ricardo Melges; Malagutti Filho, Walter
Fonte: Universidade de São Paulo. Instituto de Geociências Publicador: Universidade de São Paulo. Instituto de Geociências
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/12/2012 POR
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Diversos fatores têm contribuído para o aumento da produção mundial de resíduos sólidos urbanos, resultando em dificuldades no correto gerenciamento e disposição final ambientalmente adequada, além de ocasionar sérios problemas socioeconômicos, ambientais e de saúde pública. A contaminação de solos e águas subterrâneas por chorume nos locais de disposição dos resíduos quase sempre se faz presente, alavancando o surgimento e/ou a adaptação de metodologias para o diagnóstico ambiental destas áreas. Os métodos geofísicos, em especial o método da eletrorresistividade, são uma alternativa rápida, confiável e de baixo custo para esta finalidade. Neste artigo é reportada a metodologia adotada para o monitoramento temporal indireto da pluma de contaminação do aterro controlado do município de Rio Claro (SP). Dados de resistividade elétrica foram obtidos nos anos de 1999 e 2008, por meio do método da eletrorresistividade, empregando as técnicas da sondagem elétrica vertical e do imageamento elétrico. Em ambos os anos, foram executados ensaios semelhantes e nos mesmos locais, dentro da área do aterro. Os resultados indicaram que a pluma de contaminação apresenta valores de resistividade iguais ou menores a 50 ohm.m e se desloca segundo 2 sentidos de fluxo: o principal para sudeste e o secundário para oeste. Relativamente à primeira série de ensaios...

Structural pattern of subsidence in an urban area of the southeastern Mexico Basin inferred from electrical resistivity tomography

Arango-Galván,Claudia; Torre-González,Brenda De la; Chávez-Segura,René E.; Tejero-Andrade,Andrés; Cifuentes-Nava,Gerardo; Hernández-Quintero,Esteban
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 EN
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Most of the urban area in the Basin of Mexico is underlain by sediments of the former lakes of Chalco, Xochimilco, Mexico, Texcoco, Xaltocan and Zumpango, which offer poor foundation conditions for buildings. Water supply requirements have led to overexploitation of the aquifers, and the increased exacerbating the rate of subsidence causes housing units and roads to deteriorate. In order to understand the location of the cracking and fracturing pattern, a geophysical study using electrical resistivity tomography was performed in a populated zone of the southeastern Mexico Basin. Five two-dimensional resistivity profiles were acquired. Discontinuities in the resistive horizon (probably in extrusive igneous material) were identified. The discontinuities could be related to cracks and fractures observed on the surface which had previously damaged housing construction. A three-dimensional resistivity profile was also obtained. The 3D image confirms results obtained from 2D models, and shows a resistive layer with lateral discontinuities. The inferred fracture pattern has a preferential NW-SE direction, related to the a subsidence process produced by overexploitation of the aquifer in the area.

Estimation of soil petrophysical parameters based on electrical resistivity values obtained from lab and in-field measurements

Delgado Rodríguez,Omar; Ladrón de Guevara Torres,María; Shevnin,Vladimir; Ryjov,Albert
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2012 EN
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Knowledge of soil petrophysical parameters is very useful for agricultural and environmental impact analysis. Therefore, it is important to develop techniques and methodologies to help obtain soil petrophysical maps both quickly and inexpensively. This paper shows two techniques for estimating clay content, porosity and cation exchange capacity from electrical measurements. The first one, based on soil resistivity measurements (SRM), is performed in the laboratory. The second technique, ERT & WRM, uses the Electrical Resistivity Tomography (ERT) and groundwater resistivity measurements (WRM) in the field. A geoelectrical study was carried out in a sandy-loam site and the results were compared to those determined by particle size analysis using the Bouyoucos technique for textural analysis. The SRM technique was more accurate but slower than the ERT & WRM technique. The obtained results suggest a new application of geoelectrical methods for precision farming, both for analysis of soil samples in the laboratory using SRM technique and to evaluate large tracts of agricultural land using ERT & WRM technique.

Use of electrical resistivity tomography in the study of soil pollution caused by hydrocarbons: Case study in Puebla (Mexico)

Arrubarrena-Moreno,Manuel; Arango-Galván,Claudia
Fonte: Sociedad Geológica Mexicana, A.C. Publicador: Sociedad Geológica Mexicana, A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2013 EN
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The use of electrical resistivity tomography in the study of soils contaminated by hydrocarbons has had a substantial impact since it gives valuable information on the spatial distribution of pollutants in the subsoil. This methodology was applied to characterize an area contaminated by middle fraction hydrocarbons located at the east of the city of Puebla (central México) in order to probe its effectiveness. Additionally, chemical sampling was conducted in order to identify contaminated areas. Concentrations were determined in five samples in the zone based on the Official Mexican Standard NOM-138-SEMARNAT-SS-2003 (SEMARNAT, 2005). The geophysical survey consisted of six profiles of 20 m length, using a dipole-dipole array with a separation of four m between profiles and 50 cm of electrode spacing. Later, the geoelectrical models were computed using an inversion scheme in order to determine the resistivity distribution and its relationship with possible contamination. Results obtained from chemical sampling depicted that the contaminated area was between 0 and 1.3 m depth; three of the five analyzed samples showed a concentration above the allowed standard limit. Comparison between chemical and geophysical data allow us to assess the sensitivity of the physical property to the presence of the contaminant...

Volcano-sedimentary stratigraphy in the Valsequillo Basin, Central Mexico inferred from electrical resistivity soundings

Urrutia-Fucugauchi,Jaime; Trigo-Huesca,Alfonso; Téllez-García,Eloísa; Pérez-Cruz,Ligia; Méndez-Rivero,Fabiola
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2014 EN
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Initial results of an electrical resistivity survey of the volcano-sedimentary sequence of the Valsequillo basin in central Mexico are presented. The volcano-sedimentary deposits preserve rich paleontological, paleoclimatic and paleoenvironmental records, which include extinct megafauna remains associated with human artifacts. The report of possible 38 ka old human footprint tracks in the Xalnene tuff attracted renewed interest in the basin stratigraphy. We examine the shallow stratigraphic sequence in the Xalnene tuff outcrop plain northwest of Cerro Toluquilla volcano using vertical resistivity soundings (VES). Inversion models of VES soundings show a layered structure of high and low resistivity units, which characterize the Xalnene tuff, lacustrine and fluvial sediments and volcanic rocks. 2-D resistivity cross sections document three major units corresponding to the Xalnene tuff and sediments filling a <30 m deep basin lying on volcanic rocks. Resistivity models provide further support for the association of Xalnene tuff with the Toluquilla volcano and emplacement of the pyroclastic deposits on a shallow lacustrine environment. The resistivity cross sections constrain the thickness of the tuff layers and underlying lacustrine sediments. Observations during the data acquisition field work provide insight on the possible origin of the apparent tracks...

On the use of electrical resistivity methods in monitoring infiltration of salt fluxes in dry coal ash dumps in Mpumalanga, South Africa

Muchingami,Innocent; Nel,Jacobus; Xu,Yongxin; Steyl,Gideon; Reynolds,Kelley
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
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One of the principal environmental concerns relating to coal combustion waste disposal is the potential for groundwater contamination from salt fluxes and trace elements that may be leached into the underlying groundwater system. Since changes in moisture and salt concentrations usually provide contrasts in electrical properties against the host media, electrical resistivity methods can be used to monitor ingression of solute plumes as well as to detect any preferential flow paths within the ash medium. In this study, 2D electrical resistivity tomography was used to monitor brine (10% NaCl) water ingression through the unsaturated zone of a dry coal ash dump at a power station, Mpumalanga, South Africa. This was after the initial laboratory determination of the relation between electrical resistivity and moisture/salt content for the ash dump. The results showed that infiltration plume progression was more pronounced in the vertical direction, suggesting that moisture movement is mainly due to gravitational pull. There was no evidence of preferential flow within the ash medium, although the different infiltration rates for different sites suggested different permeability within the unsaturated zone.